The use of microRNA's (miRNA) for the study, detection, prognosis and cure of disease is growing and becoming a reliable tool toward improving human health. In this regard the immune system is an important area since T cells are greatly impacted by deletion of dicer a key RNA processing enzyme required for the generation of miRNA. To gain new insight into how miRNA impact T cell responses, mice were immunized with costimulation and adjuvant to generate potent T effector responses. We generated a cDNA library that could trace changes in miRNA derived from lymphoid tissue. Using sequencing of size-fractionated cDNA we cloned 6 potential miRNAs from this library and found candidates that possessed characteristic stem loop folding and were dicer dependent. One of these candidates, termed miR-R89, was unique compared to the others since its expression was hematopoietic specific and also regulated during immune activation. The targets and function of miR-R89 are currently unknown but our new preliminary data show that it is expressed in a T cell clone known to cause experimental autoimmune encephalitis (EAE). In Aim 1 we will use a powerful proteomic strategy to examine the effects of blocking miR-R89 on the T cell proteome followed by our bioinformatics gene targeting data and a molecular approach to validate potential target genes. In Aim 2 we will study how miR-R89 inhibition affects the initiation and progression of EAE. Thus, this R21 proposal will explore how a new miRNA can impact specific T cell function, which may lead to a novel translational approach for multiple sclerosis in humans.